Uncertainty in defence is usually disastrous, but the rivalry between goalkeepers at Old Trafford is intriguing and may even be stimulating in the long run. Nonetheless, these are unlikely to be the circumstances envisaged by Sir Alex Ferguson when he prepared for life without Edwin van der Sar, now retired, in the Manchester United line-up.

Much as managers extol competition for places, they are generally happy to see the same man between the posts week after week. United, out of circumstance more than preference, have been calling that principle into question as David de Gea and Anders Lindegaard vie for selection.

It is unlikely that the club anticipated the current situation. Ferguson might have liked to depict them as equals who each had something to prove, but the contrast was marked. While De Gea cost £18.9m from Atlético Madrid last June, a club who won the Europa League in 2010, Lindegaard was already on the United payroll as a £3.5m signing from Aalesund and had his first outing with United almost a year ago.

De Gea, however, has faltered while his rival seems invigorated after overcoming the odds. There may even be a special satisfaction to keep him buoyant as he puts the sceptics to flight for the moment. A gift for defiance is particularly welcome in goalkeepers and the Dane must be revelling in it these days.

His great countryman and United predecessor Peter Schmeichel had been scornful when the early suggestions circulated that Lindegaard could be of service at Old Trafford. "We are talking about United here," he said. "You can look at talent, you can look at young good players, [but] you don't want that, you want someone who can go in straight away and give performances in 80% of the games that the No1 choice goalkeeper will play for United."

Those remarks appear obsolete, with Lindegaard full of conviction at present. Goalkeepers, peculiarly, are supposed to be soulmates as well as rivals, perhaps because each understands the stresses the other experiences. Nonetheless, Lindegaard does not conceal his satisfaction.

He has started three games since De Gea was held accountable for the 3-2 loss to Blackburn Rovers at Old Trafford. "I don't need a [guarantee] of my position," said Lindegaard. "I enjoy every game I play for United, it is a massive privilege." The goalkeeper even sounded fleetingly as if he had appointed himself mentor to a surely crestfallen De Gea.

"I am doing everything I can to help him," said Lindegaard. "I enjoy working with him. He's a great lad. He is happy, intelligent, always with a good attitude and we have to push each other.

"We have to see the glass half full, not half empty. It has been very good for both of us. Every time we play, the last guy to wish the keeper good luck is the other keeper.

"We have a very good relationship and I enjoy working with him. He has extraordinary attributes – extremely explosive and powerful. He is only 21. His potential is massive and there is no doubt he will be United's best goalkeeper at some point. My job is to make sure it is not until I have retired. Which is [in] 10 years."

That little piece of teasing is not merely jocular. At 27, Lindegaard is far from gnarled and the ambition shines through. "I am very proud of what I have made out of this. Three years ago I was in Denmark's second division. Nobody knew my name. When I first came here nobody could pronounce it. It has been fantastic to this point and right now is not the time to relax about it, but to keep pushing on, to get better and to get the best for yourself and the club."

The circumstances are still complicated. Any notion of United alternating goalkeepers would be folly, evoking a time, for instance, when Ron Greenwood's alternating of Peter Shilton and Ray Clemence for England spoke of indecision rather than the granting of equal opportunity.

Ferguson, however, is not to be taken as a ditherer. He might like to operate a meritocracy, but it is improbable that De Gea will be shoved into the margins of his thinking. The manager, indeed, has taken steps to counteract any such notion, with the Spaniard preferred for four of the six games in the ultimately unsuccessful Champions League group campaign.

De Gea seems to be treated as a long-term investment who is also meant to hold down his place in the line-up at the moment. Nothing will come easy to him or, indeed, to Lindegaard. Each could bemoan circumstances in the back four that see the centre-half and captain Nemanja Vidic lost to injury for the season just when Rio Ferdinand, as he ages, needs the aid of the Serb more than ever.

These taxing circumstances could be the making of De Gea. Or Lindegaard.